Polyvinyl chloride resin-urea-clay composition and method of making same



United States 2,890,190 Patented June 9, 1959 2,890,190 POLYVINYL CHLORIDE RESIN-UREA CLAY COM- POSITION AND METHOD OF MAKING SAME Ross Van Volkenburgh, Berger, Tex., assignor to J. M. Huber Corporation, Burger, Tex., a corporation of v New Jersey No Drawing. Application June 14, 1955 Serial No. 515,555 8'Claims. (Cl. 26041) This invention relates to a process and to new compositions for producing stable clay-filled polyvinyl chloride resins. The invention also relates to stabilized polyvinyl chloride resin compositions containing clay fillers.

Polyvinyl chloride resins which consist mainly of polymers or copolymers of vinyl chloride and/or vinylidene chloride, have a tendency to turn brown and become embrittled when heated, for example, at temperatures of 250 F. or higher. Temperatures of that order are commonly used in the fabrication of commercial products from these resins; so, it has long been the practice to inhibit or minimize the deterioration of the resin compositions by the addition of substances known in the art as stabilizers. Examples of such stabilizers are basic lead carbonate, mixtures of barium and cadmium laurates, and organic polyesters.

While such stabilizers are effective in polyvinyl chloride resin compositions that do not contain clays, it is well known that the addition of clays to serve as a filler or pigment material causes the development of a slate or gray color when the clay-filled resin is heated. This discoloration occurs even in the presence of the usual stabilizers. Some chemical additives are known, especially certain basic organic compounds, which will prevent the development of a slate color, but such substances cause a brown discoloration of the resin, instead. A tan to brown color also is developed in polyvinyl chloride resins when they are heated after having been compounded with a finely divided neutral or basicclay produced by adding an inorganic base to an aqueous clay slurry and then filtering and drying the treated clay.

Any substantial discoloration of the clay-filled polyvinyl chloride resin manifestly is undesirable, whether the color developed be gray or brown, since it prevents the production of white or pastel colored finished products. On the other hand, it is particularly desirable to use finely divided clays as fillers or pigments for polyvinyl chloride resins, since the clays impart improved scratch and scuff resistance to the resin compositions and improve their resistance to abrasion. They also reduce the unit cost of the finished products made from the resins.

It is an object of this invention to provide clay compositions having improved properties for use as fillers or pigments in polyvinyl chloride resin compositions.

Another object is to provide a method whereby clay fillers may be incorporated in polyvinyl chloride resins processed at the usual elevated temperatures without causing the resins to become thermally discolored.

A further object of this invention is to treat and stabilize finely divided clays so that they not only will preserve the desired color and improve other properties of polyvinyl chloride resins when used therein, but also will be compatible with the resins during mixing, compounding, calendering and molding operations at temperatures up to about 350 F.

Yet another object of this invention is to provide improved color-stable products, including shaped articles, films and sheet materials, made of polyvinyl chloride resin compositions containing clay as a filler or pigment.

It has been discovered that the objects of this invention can be accomplished by incorporating a small amount of urea in a clay to be used as a filler or reinforcing pigment in polyvinyl chloride resin compositions. When a finely divided clay containing about 0.5 to 2 parts by weight of urea per parts of the clay is mixed with a polyvinyl chloride resin composition and the resulting composition is compounded and calendered or molded in the usual manner at temperatures of about 250 to 350 F., the finished products obtained show no objectionable discoloration as a result of the presence of the clay filler. Instead, they hold their desired color qualities while they are being fabricated at elevated temperatures and also under the conditions normally encountered in their use, without suffering the gray or brown discoloration that heretofore has attended the use of clay-filled polyvinyl chloride resin compositions.

Any of a wide variety of finely divided clays can be treated and used as a filler or pigment in ponlyvinyl chloride resin compositions according to the present invention. The clay use may be one of those commonly used in paper manufacture or in rubber or other plastic compositions. It may be a clay of the montmorillonite, illite or kaolin type, or of other known types. On the other hand, clays such as kaolin, which consist predominantly of kaolinite, are particularly useful for the purposes of the invention. It has been found that clayfilled ponlyvinyl chloride resin stocks and finished prod ucts having the lightest and most valuable color qualities are obtained when kaolinitic clays are treated and used in the resins according to this invention.

The final step in the processing of clays usually consists in grinding or pulverizing the clay. Urea can be conveniently incorporated with dry clay prior to the grinding, so that the ensuing grinding process in conventional equipment serves to distribute fine particles of urea in intimate contact with the particles of clay. In this way, a valuable stabilized clay composition is obtained for use in polyvinyl chloride resin compositions. If the clay has been previously ground, a similar intimate blend of fine urea particles with the clay may be pro duced by mixing the two substances in any suitable way, for example, by the use of apparatus conventionally employed for mixing finely divided solids. In order to obtain a thorough dispersion of the urea throughout the clay, the'urea should be finely ground and the two substances should be mixed together in a dry condition.

The least amount of urea giving an appreciable degree of color stabilization is usually about 0.5 part of urea per 100 parts of clay. The most advantageous practice is to treat the clay with from 0.75 to 1.50 percent of urea, by weight. Although amounts of urea larger than 2% of the clay weight can be used to obtain polyvinyl chloride resin compositions having a stable creamy-white color, the color advantage is no greater than when amounts up to 2% are used, and the resin stocks produced with such larger amounts of urea are likely to stick to the rolls of the compounding mill at milling temperatures of 300 to 340 F. This tendency to stick to the mill rolls makes it difficult to handle the stocks, so urea additions in excess of about 2% of the clay weight generally are undesirable.

Although no precise explanation can now be given for the effects obtained according to this invention, it appears that the urea has a stabilizing action which it exerts at the surfaces of the clay particles incorporated in the polyvinyl chloride resin. The action of the urea-treated clay appears to be quite unlike the action of conventional stabilizers for vinyl chloride polymers. The effect obtained is quite surprising, since the addition of urea to vinyl chloride polymers in the absence of clay fillers and of known stabilizers causes the polymers to turn brown. Moreover, urea additions in the absence of clay will cause a brown discoloration even though certain known stabilizers are present in the polyvinyl chloride resin composition.

Preferred ways of practicing this invention and the advantages achieved by its use are further illustrated in gray products resulted after 15 minutes of milling. Samples molded as described above were also dark slate colored.

The compositions of Formulas C and D remained the following examples. Proportions of various ingredi- 5 cream-colored on the mill even after 30 minutes of millents in the examples are expressed as parts or percentages ing. Samples molded at 340 F. were also cream-colored. by weight. The ureatreated clays employed in the examples were prepared in each instance by premixing the Example 2 cla with mir ture tw i c t li ro iigli zi l i a ir iiiiid giiri din 'l l l l l lSi 1O Vanous sampl-es of days were employed In compo. a inch slot screen y g g tions corresponding to Formula A of Example 1. These cl The molded test samples referred to in the examples s caused th-polyvmyl Chloride clay compoimon to ar en on the mill. The degree and shade of discolorawere produced by the use of usual commercial practices tion varied with the clay and its in as noted in the for mixing the components of the polyvinyl chloride resin following table g compositions and for molding the composit ions into test Samples of the Same clays treated with 1.25% of urea samples. A mixture of the polyvinyl chloride resin and 1 a so were employed in compositions of the same formula. the resin stabilizer was first prepared in a glass container. A

s shown in the following table, the samples obtained Then the liquid plasticizers were added and mixed in.

. iom compositions containing the urea-treated clays in all About one-half of the clay was then added and mixed cases were consistently lighter in color than those obwell before adding and mixing the remainder of the clay. 2O tained from the corms ondin untreated 1a 8 The complete mixture was then added to the steel rolls p g c y of a six inch steam-heated mill while the rolls were maintained at a temperature of 300 to 310 F. The resin C1 C1 fM 1d d I g compositions were held and milled on the rolls for or ay 0 om o e Samp e i n gminutes before sheeting oif and cooling. Molded sam- 25 ples were obtained by pressing samples of the milled South Carolinasoftlmolinuntreatei 9 stocks in 2 x 2 x 0.1 inch electrically heated molds preggg g kaolin urea 23 heated and maintained at 340 F. The samples were South Carolina hard kaolin 1m Dark Slate 4 heated in the molds for one minute at low pressure, then treated- South Cai'olma hard kaolin urea- Cream 22 for seven minutes at high pressure, and then they were 00 treated,

English kaolin untreated G 'sh-b vn 6 cooled. to room teimperafture. undel: high pressure m the English kaolin urea-treated Li g li t greeiii li-browm 10 following seven minutes by circulating cold Water through German kaolin untreated Tan 13 the mold platens. The molded samples were removed German kaolm m'efi'treated Light 17 from the molds, the colors were noted, and the percent reflectance of white light from the surface of each sample Example 3 was measured by the use of a calibrated Densichron reflectance meter. Apart from color differences, the sur- As shown in Examples 1 and 2, the stabilizer comface conditions of the various sets of samples were similar posed of barium and cadmium laurates did not prevent whether or not the samples contained urea with the clay; the gray color from developing in polyvinyl chloride so only the colors of the samples afiected the amounts resins containing clay. Other stabilizers were equally of light reflectance. The greater percent of reflectance ineffective, as shown by tests summarized in the followdenotes a lighter color. ing table:

Formula A B G D E F Polyvinyl chloride 100 100 100 100 100 100 Plasticizer (Dioctyl phthalate) 60 60 60 60 Untreated kaolin 160 160 160 Kaolin containing 1.25% urea 160 160 160 Stabilizer (Barium and Cadmium Laurates) (Paraplex Polyester) Stabilizer (Basic lead carbonate) Color of molded sample Stabiliz er 1 Rohm and Haas 00. (polyester resins based on long chain polybasic acids esterifled with polyhydric alcohols such as glycol or ethylene glycol).

Example 1 A commercial grade of kaolin clay was incorporated in polyvinyl chloride resin compositions of the types used for the manufacture of floor tiles, according to the following formulations:

Example 4 The effects of varying the amount of urea used to treat a given amount of clay are demonstrated by the following data. Stocks were prepared by the usual procedure from parts of polyvinyl chloride, 60 parts of plasticizer (dioctyl phthalate), 1.2 parts of stabilizer (barium and cadmium laurates) and the following urea-treated clays.

Parts] Behavior on Color of Treated Clay 00 Milling Molded PVC Sample Kaolin+0.375% urea Gray-tan. Kaoliu+0.625% urea Do. Kaolin+1.25% urca Cream Kaolin+1.5% urea D0. Kaolin+3.0% urea.-. Do. Kaolin+6.0% urea D0.

Example 5 The unique ability of urea-treated clay to overcome the discoloration of clay-filled polyvinyl chloride resin compositions is shown by the following comparisons of the varied from as little as a trace up to as much as 250 parts or more per hundred parts of the resin, depending upon the other materials used and the properties desired in the finished product. Moreover, as is well known in the art,

result obtained from urea-treated clay with the results 5 varicius plasticizers Stabilizers .Coloring materials fillers obtained from the use of a similar clay treated with varilubncatlng i other chemlcals may be used a the ous other substances known to be stabilizers for polyvinyl l q m Whlch they may be used are Subject to chloride resins. The treated clays were compared in Wlde i stocks corresponding to Formula A, Example 1, and were What IS claimed 15: mixed and molded in the usual procedure. 10 T method of .producmg. clay-filled polyvinyl chloride resln composltlon, whlch comprlses mcorporating in a polyvinyl chloride resin composition a Chemical Used in Treating Clay fififig figi3j2tliif finely divided clay and urea in a small amount sufficient y to inhibit thermal discoloration of said composition in the presence of the clay. e e Gray- 2. The method of producing a color-stable clay-filled iii ri siii c i iiiiiiij 'ihrsjjIIIIII ii i? L i ili than. P y y chloride resin composition, Which comprises symmctricel-dibutylhrea- Ten brOWH- incorporating in a polyvinyl chloride resin composition a 3j; f?}f jf i igfinely divided clay and about 0.5 to 2 parts by weight of ASymmetrical-diphenylure 1.25 Gray. urea per 100 parts Of the clay.

3. The method of producing light-colored abrasion- Diblltyleminc Light brown resistant products from polyvinyl chloride resin compo- 21 35533 5???- 1 i1 gigf igiy sitions, which comprises incorporating with a polyvinyl Amm0niege1 r y. chloride resin composition a finely divided mixture of 3.333333 153 3333 II fifgi g gggf brown 25 a clay and about 0.5 to 2 parts by weight of urea per 100 Aqueous calcium hydroxide D0. parts of the clay, and milling the resulting composition Urea Pale Cream at a temperature between 250 and 350 F.

4. A polyvinyl chloride resin composition containing siii u iii fii loiififiii n ii sill gisiiini fig rid iiled vi' eiiirnsi iii a finely divided y and urea in a ll nt uflicient Produce basic Slurriesto inhibit thermal discoloration of said composition in the Example 6 presence of the clay.

The effects of urea on polyvinyl chloride polymers and 5. A polyvinyl chloride resin composition having intipolyvinylidene chloride polymers in the absence of clay mately dlspersed thereln a finely dlvlded clay and about filler are shown in the following table. Samples were to 2 Parts Py e ght of urea per 100 parts of the clay. prepared in the usual procedure except that the clay was P Y Y Chloride e 1n compesltlon comprising omitted. The percent reflectance was obtained from the a resln from the group conslstmg 0f P y and ld d l polymers of vinyl chloride and vinylidene chloride and A B o D E F G liglfiglifillf fifixsn 100 100 100 100 100 100 100 Plastlelzer (Dloctyl phthalate) 50 50 50 50 50 50 i t lgillzer (Ba and. 0d laurates) 2 0 2.0 5:8 n 2.0 ill Millin time at sou-310 F./M1n so '30 n 80 1 15 Color of molded samples Brown Brown Clear 0198! Brown Brown 01981 Percent reflectance 3 2 22 17 4 32 The above data demonstrate that urea is not a heat a finely divided mixture of a y and about t0 2 stabilizer for polyvinyl chloride resins. Instead, urea parts y welght of urea p 100 Parts of the claycaused the resins to become darker than when no urea 50 mcthqd of producing a color-Stable clay-filled was present. The barium and cadmium laurates did p y ch1c r1dc resin composition, which p ises stabilize the resin and even reduced the amount of dis- IHCOI'POTaPIIg 111 a P y y chloride resin composition coloration caused by the urea itself, but stock D conf y Y kaOllll and urea a S ll amount Sufiitaining both the stabilizer and urea was darker than stock 9 to mhiblt thermal discoloratlon of Said composition C which contained the stabilizer alone. 111 the P P 0f the f The urea-treated clays disclosed herein are valuable as A P y y Phlorlde re$111 COmPOSItiOII containing fillers for vinyl chloride polymers and vinylidene chloly divided kaolm a urea in a Small nt llfi'icient ride polymers, and for copolymers of these two monomers mhlbit thermal dISCQIOI'afiOII of said COmPOSifiOII in with each other. The treated clays may also be used to the Presence of the K301111- advantage with other copolymers in which the total content of polyvinyl chloride or polyvinylidene chloride, or References In the file of thls Patent of both, exceeds about 50 percent by weight. UNITED STATES PATENTS It will be understood that the manner of use of this invention is not limited to the particular formulations 22 5 et 1 5 6 in the eXamPlesexample the amwnt 2I311i233 JasnieiQQt QL IIIII Feb: 16: 1943 treated clay to be used in the resin compositions may be 

